4340 VAR is standard aircraft quality 4340 given a vacuum arc remelt. Remelting under vacuum strips dissolved gas and non metallic inclusions and solidifies the ingot progressively, producing a cleaner and more uniform structure than air melted material.
That cleanliness matters most where fatigue governs. Inclusions act as crack initiation sites, so a vacuum melted bar of the same chemistry and hardness routinely shows better fatigue life, better transverse ductility and more consistent ultrasonic results than its air melted equivalent.
We stock 4340 VAR in bar and forging billet with full melt traceability, and supply it in the annealed, normalized and tempered, or quenched and tempered condition your specification calls out.
Sizes and stock
- Round bar: through 12" DIA
- Flat bar: through 12" THK
- Sheet / plate: through 6" THK
- Custom shapes and forgings: per request
Processing capabilities
- Vacuum melted (VAR / VIM-VAR) stock with full melt traceability
- Normalize, anneal, quench and temper to the ordered condition
- Saw cutting, trepanning, gun drilling and rough machining
- Magnetic particle and ultrasonic inspection to AMS 2301 / AMS 2154 on request
Specifications
Material is released to the applicable specification with mill test reports and, on request, independent lab verification.
Why engineers specify 4340 / 4340 VAR
- Vacuum arc remelted for low inclusion content and gas levels
- Improved fatigue life and transverse properties over air melt
- Cleaner ultrasonic response for critical rotating and structural hardware
- Same well understood heat treat response as standard 4340
Nominal chemistry
Percent by weight, nominal composition per the governing specification. The mill test report for your heat is the controlling document.
Typical mechanical properties
| Condition | Tensile strength | Yield strength | Elongation | Hardness |
|---|---|---|---|---|
| Q&T, 180 ksi class | 180 ksi min | 163 ksi min | 10% min | - |
| Q&T, 200 ksi class | 200 ksi min | 176 ksi min | 10% min | - |
| Q&T, 260-280 ksi class | 260 ksi min | 215 ksi min | 8% min | - |
Typical published values for reference only, not for design. Properties vary with section size, product form and processing. Order to the specification and condition your drawing requires.
Typical applications
- Landing gear and gear pins
- Rotating shafts and couplings
- Fracture critical airframe fittings
- High cycle fatigue tooling
Fabrication notes
Machining
Best machined in the annealed or normalized-and-tempered condition, then heat treated to final strength. Rough machining before hardening, with a finish pass after temper, controls distortion on long or thin sections. We can supply rough turned, trepanned or gun drilled stock so your first operation starts closer to net shape.
Welding
Weldable with low hydrogen practice, preheat appropriate to carbon equivalent and section size, and a post weld stress relief or full re-heat treat. For high strength conditions the weld and heat affected zone should be re-treated to restore properties.
Forming
Hot work in the annealed condition. Cold forming is limited at high hardness, so bend and form before hardening and follow with stress relief where the geometry is tight.
4340 / 4340 VAR compared with similar grades
4340 air melt
Same chemistry and strength, lower cleanliness, usually acceptable where fatigue is not the governing mode.
300M
Higher strength ceiling for landing gear, also vacuum melted.
Designations and cross reference
- Material family
- Alloy Steels
- UNS number
- G43400
- Werkstoff (W.Nr)
- 1.6565
- EN designation
- 40NiCrMo8-4
Working from an obsolete, foreign or superseded designation? Send it over and we will cross reference it to a current grade and specification.
Quality, testing and traceability
Supplied aircraft quality with mill test reports, melt and heat traceability, and, on request, magnetic particle inspection to AMS 2301 or AMS 2300, ultrasonic inspection to AMS 2154, chemical assay, hardness and full mechanical testing.
We are AS9100D and ISO 9001:2015 registered. If our stock does not already carry the inspection your specification requires, we can quote the material with that work performed. More on our quality system
Available forms
Custom sizes converted from billet, plus saw cut, waterjet and near-net blanks. See custom conversions
4340 / 4340 VAR frequently asked questions
What is 4340 / 4340 VAR?
4340 VAR is standard aircraft quality 4340 given a vacuum arc remelt. Remelting under vacuum strips dissolved gas and non metallic inclusions and solidifies the ingot progressively, producing a cleaner and more uniform structure than air melted material.
What forms is 4340 / 4340 VAR available in?
We supply 4340 / 4340 VAR in bar, sheet, plate, forging. Custom sizes are converted from billet, and we can provide saw cut, waterjet or near net blanks so material arrives closer to your finished part.
What is the UNS or equivalent designation for 4340 / 4340 VAR?
4340 / 4340 VAR is designated UNS G43400, Werkstoff 1.6565, EN 40NiCrMo8-4. If your drawing calls out an obsolete or foreign designation we can cross reference it and confirm the equivalent before you order.
What specifications can 4340 / 4340 VAR be supplied to?
Commonly ordered specifications include AMS 6414, AMS 6415, AMS 6454, AMS 6417, UNS G43400. Material is released to the specification and condition on your purchase order, with mill test reports supplied as standard.
What conditions can 4340 / 4340 VAR be ordered in?
We can supply Q&T, 180 ksi class, Q&T, 200 ksi class, Q&T, 260-280 ksi class. If our stock is not already in the condition you need, we can quote it with the heat treatment performed before shipment.
Can you cut 4340 / 4340 VAR to size?
Yes. Saw cutting, waterjet, laser and shearing are available, along with trepanning, gun drilling, lathe turning and CNC machining, so you can order blanks or rough machined pieces rather than full lengths.
Do you provide test reports and additional testing on 4340 / 4340 VAR?
Every order ships with mill test reports and heat traceability. If your print calls for ultrasonic inspection, penetrant dye, magnetic particle, chemical assay, micrography, hardness or mechanical testing and our stock does not already carry it, we can quote the material with that work performed.
Can 4340 / 4340 VAR be supplied to DFARS domestic melt requirements?
Tell us at quote stage if the order is DFARS or domestic melt restricted and we will confirm availability against that requirement before you commit.
What do you need to quote 4340 / 4340 VAR?
Grade, form, dimensions, quantity, specification and condition, plus any testing or certification requirements and the date you need it. Send a drawing if you have one. Quotes are typically ready within 24 hours.
How does 4340 / 4340 VAR compare with 4340 air melt?
Same chemistry and strength, lower cleanliness, usually acceptable where fatigue is not the governing mode.